The long-term objective of this proposal is to develop a prototype scanning system from which we can manufacture and profitably market novel and advanced ultrasound scanning systems for the imaging, tissue characterization and diagnosis of cancer and other diseases. It will give superior images of obstetrical conditions, vascular disease, liver disease, and other abdominal conditions. This advanced system is based on extending the capabilities of a new imaging method we have developed and tested called acoustic inverse-scattering tomography. This method provides accurate, high-resolution, quantitative images of speed-of-sound c(x), density rho(x), absorption alpha(x), acoustic impedance Z(x), and compressibility Kappa(x). The scanner will also support a high-resolution synthetic-focusing mode capable of four to six times the spatial resolution of present scanners. The inverse-scattering images c(x) and alpha(x) will allow us to correct the synthetic-focus images for refraction and absorption artifacts. The scanner will also have a real-time search-imaging mode with spatial resolution equal to or better than that of present scanners. The scanner architecture will let us, after Phase II, add components to use the above modes simultaneously with true blood-flow vector velocity imaging (V(x) = Vx,Vy,Vz)).